Projection display device

ABSTRACT

An illuminating optical system for focusing a radiant light of a light source ( 1 ) onto a reflecting light valve ( 6 ) and a projection lens ( 7 ) for magnifying and projecting a reflected light from the reflecting light valve ( 6 ) onto a screen are provided, a diaphragm ( 31 ) is disposed at a substantially conjugate position of an entrance pupil of the projection lens ( 7 ) on an optical path of the illuminating optical system, the diaphragm ( 31 ) has an opening whose area is changed by a light-shielding member, and a shape of a shielded portion of the diaphragm ( 31 ) shielded by the light-shielding member is rotationally asymmetric to an optical axis ( 12 ) of the illuminating optical system. Accordingly, shielding of necessary light can be better avoided compared with a diaphragm for changing the light-shielding area in a rotationally symmetric manner, for example, a diaphragm for narrowing the opening concentrically, making it possible to improve contrast performance while minimizing brightness reduction.

TECHNICAL FIELD

The present invention generally relates to a projection-type displayapparatus that magnifies an optical image formed on a light valve andprojects it onto a screen.

BACKGROUND ART

There has been a conventionally well-known method for obtaining alarge-screen image, in which an optical image corresponding to a videosignal is formed on a light valve, irradiated with light, and thenmagnified and projected onto a screen by a projection lens. The use of areflecting light valve as the light valve can achieve both a highresolution and a high pixel aperture ratio, making it possible todisplay a highly-bright projected image with highly efficient lightutilization.

As a conventional example, FIG. 10 illustrates a configuration of anoptical system of a projection-type display apparatus using a reflectinglight valve. An illuminating optical system for focusing andilluminating light emitted from a lamp 1 as a light source onto areflecting light valve 6 includes a concave mirror 2, a quadratic rodprism 3 whose cross-section has substantially the same aspect ratio asan effective display surface of the reflecting light valve 6, acondenser lens 4 and a focusing mirror 5.

The concave mirror 2 has a reflecting surface with an ellipticalcross-section and has a first focus and a second focus. The lamp 1 isdisposed so that the center of its light-emitting body is in thevicinity of the first focus of the concave mirror 2, and the rod prism 3is disposed so that its light entrance surface is in the vicinity of thesecond focus of the concave mirror 2. In addition, the concave mirror 2is obtained by forming on an inner surface of a glass base an opticalmultilayer film that transmits infrared light and reflects visiblelight.

Light emitted from the lamp 1 is reflected and focused by the concavemirror 2 and forms an image of the light-emitting body of the lamp 1 atthe second focus of the concave mirror 2. The light-emitting body imageof the lamp 1 is brightest near the center, which is close to an opticalaxis, and rapidly becomes darker toward the periphery, and thus there isununiformity in brightness. To solve this problem, the entrance surfaceof the rod prism 3 is disposed in the vicinity of the second focus,incident light is subjected to multiple reflections on a side surface ofthe rod prism 3 to achieve brightness uniformity, and the exit surfaceof the rod prism 3 serves as a secondary surface light source to form animage on the reflecting light valve 6 by the subsequent condenser lens 4and focusing mirror 5, thereby securing uniformity of the illuminatinglight.

Herein, the operation of the reflecting light valve 6 will be describedreferring to FIG. 11. The reflecting light valve 6 controls a travelingdirection of light according to a video signal and forms an opticalimage by a change in a reflection angle. Mirror elements 21corresponding respectively to pixels are formed in a matrix pattern, andeach of the mirror elements 21 inclines ±θ° with respect to a plane 22perpendicular to the optical axis of the projection lens by an ON signalfor a white display and an OFF signal for a black display. After passingthrough a cover glass 23, an illuminating chief ray 24 enters and isreflected by the mirror element 21 and leaves the cover glass 23 again.

As shown in FIG. 11A, first, the incident angle of the illuminatingchief ray 24 is set such that, at the time of the ON signal, an ON lightchief ray 25 is reflected and travels along a direction perpendicular tothe plane 22, that is, the optical axis of the projection lens. In thiscase, the illuminating chief ray 24 and the ON light chief ray 25 forman angle of 2θ. On the other hand, as shown in FIG. 11B, at the time ofthe OFF signal, an OFF light chief ray 26 is reflected and travels alonga direction not reaching the projection lens, and the illuminating chiefray 24 and the OFF light chief ray 26 form an angle of 6θ.

As shown in FIG. 10, an illuminating light 8 entering the reflectinglight valve 6 reaches the projection lens 7 as ON light 9 at the time ofthe ON signal or travels outside an effective diameter of the projectionlens 7 as OFF light 10 at the time of the OFF signal. By controlling thetime allocation of the ON light 9 and the OFF light 10 according to thevideo signal as described above, a projected image is formed on thescreen.

However, reflected light generated at an interface of the cover glass 23shown in FIG. 11 and the air as an external medium travels as unwantedreflection light 11, which is shown as hatching in FIG. 10, andpartially enters the projection lens 7. Since this unwanted reflectionlight 11 travels similarly in both times of ON/OFF signals, itconsiderably reduces the quality of black display especially at the timeof OFF traveling, causing a deterioration of contrast performance.

DISCLOSURE OF INVENTION

It is an object of the present invention to solve the conventionalproblem described above and to provide a projection-type displayapparatus that improves contrast performance while avoiding shielding ofnecessary light so as to minimize brightness reduction.

In order to achieve the above-mentioned object, a projection-typedisplay apparatus of the present invention includes a light source, areflecting light valve, an illuminating optical system for focusing aradiant light of the light source onto the reflecting light valve, and aprojection lens for magnifying and projecting a reflected light from thereflecting light valve onto a screen. A diaphragm is disposed at one ofa position of an entrance pupil of the projection lens and asubstantially conjugate position of the entrance pupil, the diaphragm isprovided with an opening for shielding a part of the radiant light ofthe light source, and a shape of the opening is rotationally asymmetricto an optical axis of the illuminating optical system or the projectionlens.

In accordance with the projection-type display apparatus describedabove, it becomes possible to improve the contrast performance whileavoiding shielding of necessary light so as to minimize the brightnessreduction.

It is preferable that the projection-type display apparatus describedabove further includes a light-shielding member, and a moving system ofthe light-shielding member. The shape of the opening of the diaphragm isa shape shielded by the light-shielding member, the shape shielded bythe light-shielding member is rotationally asymmetric to the opticalaxis of the illuminating optical system or the projection lens, and themoving system can change an area of the opening by displacing thelight-shielding member. In accordance with the above-describedprojection-type display apparatus, since shielding of necessary lightcan be better avoided compared with a diaphragm for shielding light in arotationally symmetric manner, for example, a diaphragm for narrowingthe opening concentrically, it is possible to improve contrastperformance while minimizing brightness reduction. Moreover, thecontrast performance and the optical output can be adjusted suitably.

Also, it is preferable to include further a prism for reflecting anilluminating light from the illuminating optical system toward thereflecting light valve and transmitting the reflected light from thereflecting light valve. In accordance with the above-describedprojection-type display apparatus, a compact illuminating optical systemcan be constructed, and unwanted reflection light generated at aninterface of the prism can be cut while minimizing the brightnessreduction.

Further, it is preferable that the number of the reflecting light valvesis three, and the projection-type display apparatus further includes afirst prism for reflecting an illuminating light from the illuminatingoptical system toward the reflecting light valves and transmitting thereflected light from the reflecting light valves, and a second prism forseparating the illuminating light into three components of primarycolors of red, blue and green and combining into one the threecomponents that are reflected by the corresponding reflecting lightvalves. In accordance with the above-described projection-type displayapparatus, a high-resolution full-color projected image can bedisplayed, and unwanted reflection light generated at interfaces of thefirst prism and the second prism can be cut while minimizing thebrightness reduction.

Moreover, it is preferable that the reflecting light valve has an imageformation surface and a transparent plate that is disposed on an exitside of the image formation surface and in parallel with the imageformation surface.

Furthermore, it is preferable that the reflecting light valve is formedof a plurality of mirror elements that are arranged in a matrix patternand control a reflecting direction of light according to a video signal.

Additionally, it is preferable that an illuminating light from theilluminating optical system obliquely enters the reflecting light valve,and that, when a reference position is a position of the light-shieldingmember at which a periphery of the illuminating light and that of anunwanted reflection light of the reflecting light valve come closest toeach other, the light-shielding member can be moved in one directionfrom the reference position toward the optical axis by the moving systemand a continuous movement in the one direction enlarges alight-shielding area of the diaphragm. In accordance with theabove-described projection-type display apparatus, the unwantedreflection light from the reflecting light valve can be cut graduallyfrom an optical axis side.

It also is preferable that the shape of the opening of the diaphragm iscircular in an opened state.

Further, it is preferable that a shielded portion shielded by thelight-shielding member has a substantially part-circular shape. Inaccordance with the above-described projection-type display apparatus,it is easy to form the shape of the shielded portion that isrotationally asymmetric to the optical axis.

Moreover, it is preferable that a side of the light-shielding member isa straight line that is parallel with a horizontal line passing througha point on the optical axis when the diaphragm is seen in a planedirection, and the shielded portion surrounded by the parallel straightline and an internal circumference of the opening of the diaphragm hasthe substantially part-circular shape.

Furthermore, it is preferable that a shielded portion shielded by thelight-shielding member has a substantially crescent shape. In accordancewith the above-described projection-type display apparatus, it is easyto form the shape of the shielded portion that is rotationallyasymmetric to the optical axis.

Additionally, it is preferable that the light-shielding member has acircular opening, the shielded portion is formed by shifting a center ofthe circular opening with respect to that of the opening of thediaphragm, and the shielded portion surrounded by an internalcircumference of the circular opening of the light-shielding member andthat of the opening of the diaphragm has the substantially crescentshape.

It also is preferable that the light-shielding member has an openingwhose inner diametral dimension is changeable and whose center isshifted with respect to the opening of the diaphragm, the shieldedportion surrounded by an internal circumference of the opening of thelight-shielding member and that of the opening of the diaphragm has thesubstantially crescent shape, and an area of the shielded portion ischanged by changing the inner diametral dimension of the opening of thelight-shielding member.

Further, it is preferable that when an upper portion is a part of theopening of the diaphragm above a horizontal line passing through a pointon the optical axis and a lower portion is a part thereof below thehorizontal line in a case where the diaphragm is seen in a planedirection, the opening of the diaphragm is shielded by thelight-shielding member gradually from one of the upper portion and thelower portion toward the other so that a light-shielding area enlarges.

Moreover, it is preferable that a surface of the light-shielding memberis formed of a metal or a dielectric multilayer film that reflects anincident light with a reflectance of at least 80%. In accordance withthe above-described projection-type display apparatus, the amount ofabsorbed light can be suppressed, making it possible to preventperipheral optical components from being damaged by radiant heat due tothe rising surface temperature of the shielded portion.

Furthermore, it is preferable to include further a control system forcontrolling how much the light-shielding member is displaced by themoving system. The control system controls a light-shielding amount ofthe diaphragm so as to change according to a level of an input videosignal. In accordance with the above-described projection-type displayapparatus, for example, by giving priority to the contrast and thehigher level of black in darker scenes and giving priority to the higherlevel of white in brighter scenes, it is possible to obtain a displayperformance with enhanced contrast.

Additionally, it is preferable that a light-shielding amount of thediaphragm is controlled from an outside of the apparatus. In accordancewith the above-described projection-type display apparatus, it ispossible to select suitably a projected image in which the brightness isimportant or that in which the contrast is important according to anintended use.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic configuration of a projection-type displayapparatus according to a first embodiment of the present invention.

FIG. 2 shows a schematic configuration for describing diaphragmpositions according to an embodiment of the present invention.

FIG. 3A shows a schematic configuration of a first diaphragm accordingto an embodiment of the present invention.

FIG. 3B shows a schematic configuration of a second diaphragm accordingto an embodiment of the present invention.

FIG. 3C shows a schematic configuration of a third diaphragm accordingto an embodiment of the present invention.

FIG. 4A shows a relationship between a light-shielding amount of adiaphragm and a contrast ratio in a projection-type display apparatusaccording to an embodiment of the present invention.

FIG. 4B shows a relationship between the light-shielding amount of thediaphragm and an optical output in the projection-type display apparatusaccording to an embodiment of the present invention.

FIG. 5 shows a schematic configuration of a projection-type displayapparatus according to a second embodiment of the present invention.

FIG. 6 shows a schematic configuration of a projection-type displayapparatus without a diaphragm according to a comparative example.

FIG. 7 shows a schematic configuration of a projection-type displayapparatus according to a third embodiment of the present invention.

FIG. 8 shows a structure of a color separation/combination prismaccording to the third embodiment of the present invention.

FIG. 9 shows a schematic configuration of a projection-type displayapparatus without a diaphragm according to a comparative example.

FIG. 10 shows a schematic configuration of an example of a conventionalprojection-type display apparatus.

FIG. 11A illustrates an operation of a reflecting light valve at thetime of an ON signal.

FIG. 11B illustrates the operation of the reflecting light valve at thetime of an OFF signal.

BEST MODE FOR CARRYING OUT THE INVENTION

The following is a description of embodiments of the present invention,with reference to the accompanying drawings.

FIRST EMBODIMENT

FIG. 1 shows a schematic configuration of a projection-type displayapparatus according to a first embodiment of the present invention. Inthis figure, numeral 1 denotes a lamp serving as a light source, numeral31 denotes a diaphragm, numeral 6 denotes a reflecting light valve, andnumeral 7 denotes a projection lens. Also, an optical system constitutedby a concave mirror 2, a rod prism 3, a condenser lens 4 and a focusingmirror 5 is collectively called an illuminating optical system. Numeral12 indicates an optical axis of the illuminating optical system.

The reflecting light valve 6 serving as an image forming member hasmirror elements 21 formed in a matrix pattern, each of which correspondsto a pixel, controls a traveling direction of light according to a videosignal and forms an optical image by a change in a reflection angle asdescribed referring to FIG. 10. The concave mirror 2 is an ellipticalsurface mirror that has a reflecting surface with an ellipticalcross-section, and has a first focus and a second focus.

A xenon lamp may be used as the lamp 1, which is disposed so that thecenter of its light-emitting body is in the vicinity of the first focusof the concave mirror 2, and the rod prism 3 is disposed so that itslight entrance surface is in the vicinity of the second focus of theconcave mirror 2. In addition, the concave mirror 2 may be obtained byforming on an inner surface of a glass base an optical multilayer filmthat transmits infrared light and reflects visible light.

The rod prism is a quadratic prism whose light entrance and exitsurfaces have the same aspect ratio as an effective display surface ofthe reflecting light valve 6, and may be made of quartz glass, which hasan excellent heat resistance, because it is to be disposed at a positionon which radiant light from the lamp 1 is focused. The light-emittingbody image of the lamp 1 focused by the concave mirror 2 is formed nearthe entrance surface of the rod prism 3. The light-emitting body imageof the lamp 1 focused by the concave mirror 2 is brightest near thecenter, which is close to the optical axis 12, and rapidly becomesdarker toward the periphery, and thus there is brightness ununiformitywithin the surface.

On the other hand, since a flux of rays that has entered the rod prism 3is subjected to multiple reflections by a side surface of the rod prism3 so that the light-emitting body image is finely divided and overlappedas much as the number of reflected times and then illuminated, uniformbrightness is achieved at the exit surface of the rod prism 3. In thismanner, the effects of fine division and overlapping of thelight-emitting body image of the lamp improve the uniformity in keepingwith an increase in the number of times of reflections in the rod prism3. Thus, the degree of uniformity depends on the length of the rod prism3. In the present embodiment, the length of the rod prism 3 was designedsuch that a peripheral illuminance is at least 90% of a centralilluminance on the screen.

The exit surface of the rod prism 3 where the brightness has been madeuniform as above is used as a secondary surface light source to form animage under a magnification that matches an effective display area ofthe reflecting light valve 6 by the subsequent condenser lens 4 andfocusing mirror 5, making it possible to both secure a light focusingefficiency and improve the uniformity. The light emitted from the lamp 1is focused by the illuminating optical system, and illuminating light 32enters the reflecting light valve 6.

ON light 33 corresponding to the white display in the illuminating light32 that has entered the reflecting light valve 6 enters the projectionlens 7 and then is magnified and projected onto a screen (not shown). Onthe other hand, OFF light 34 corresponding to the black display travelsoutside an effective diameter of the projection lens 7 and does notreach the screen.

In the following, the positional relationship of optical members will bedescribed more specifically referring to FIG. 2. The projection-typedisplay apparatus in FIG. 2 is shown as a view developed such that theoptical axis in the configuration of FIG. 1 lies on the same line forfacilitating understanding of the positional relationship of the opticalmembers.

In other words, the focusing mirror 5 as a reflecting element in theconfiguration shown in FIG. 1 is replaced by a lens 5 a as atransmitting element, and the reflecting light valve 6 as a reflectingelement in FIG. 1 is replaced by a light valve 6 a as a transmittingelement. In FIG. 2, the flux of rays shown by hatching is an on-axisflux of rays 90, and numerals 91 and 92 each indicates an off-axis fluxof rays.

The light-emitting body image of the lamp 1 is formed on the entrancesurface of the rod prism 3 by the elliptical surface mirror 2. The lightpassing through the rod prism 3 repeatedly is subjected to multiplereflections on an inner surface of the rod prism 3, so that itsbrightness is made uniform on an exit surface side.

When the exit surface of the rod prism 3 is a secondary surface lightsource image, this light source image is formed on the light valve 6 aby the lenses 4 a and 5 a and further formed on the screen (not shown)by the projection lens 7. In other words, the exit surface of the rodprism 3 and an optical image formation surface of the light valve 6 aare in a conjugate relationship, and the optical image formation surfaceof the light valve 6 a and a screen surface also are in a conjugaterelationship.

On the other hand, a diaphragm 31 a corresponds to the diaphragm 31 inFIG. 1 and is disposed between a lens 4 a and the lens 5 a on an opticalpath of the illuminating optical system. A diaphragm 93 is disposed inthe projection lens 7. The diaphragm 31 a and the diaphragm 93 areaperture stops for determining the size of cross-sections of the on-axisflux of rays 90, the off-axis flux of rays 91 and the off-axis flux ofrays 92. The diaphragm 93 is disposed at a position of an entrance pupilof the projection lens 7, and the diaphragm 31 a is disposed at asubstantially conjugate position of the diaphragm 93.

Incidentally, although the optical axis does not lie on the same line inthe configurations of FIG. 1 and FIG. 5 and thereafter according torespective embodiments, conjugate relationships similar to those in FIG.2 are achieved. Further, in these figures, the off-axis flux of rays isomitted for describing an effect of unwanted light.

FIGS. 3A to 3C illustrate specific examples of the diaphragm 31 shown inFIG. 1. In each figure, a fixed diaphragm 36 has an opening throughwhich light passes, and its position to be disposed and its openingshape are fixed. The diaphragm is constituted by a combination of thisfixed diaphragm 36 and a light-shielding plate 37 a, 37 b or 37 cserving as a light-shielding member.

The light-shielding member according to the present embodiment can bedisplaced by a moving system, whereby a light-shielding area can bechanged. This displacement of the light-shielding member includesmovement of the position of the light-shielding member and a change inshape of the light-shielding member itself such as a change in anopening area of the light-shielding member.

The diaphragm 31 a shown in FIG. 3A includes the fixed diaphragm 36 andthe light-shielding plate 37 a serving as the light-shielding member. Inthis figure, a part of the opening of the fixed diaphragm 36 is shieldedby the light-shielding plate 37 a. The hatched portion is a shieldedportion (for example, a portion indicated by numeral 38 a in the rightend figure; the same applies to numerals 38 b and 38 c in FIGS. 3B and3C).

As shown in this figure, the light-shielding area increases with alowering of the light-shielding plate 37 a. The light-shielding plate 37a has a side 37 d, which is a straight line parallel with a horizontalline 39 passing through a center 36 a of the opening of the fixeddiaphragm 36 (a point on the optical axis 12 in FIG. 1). Accordingly,the shielded portion surrounded by the side 37 d and an internalcircumference of the opening of the fixed diaphragm has a substantiallypart-circular shape. This remains the same while the light-shieldingplate 37 a is moved downward, and the shielded portion achieves acomplete semi-circular shape when the side 37 d and the horizontal line39 match.

With regard to the diaphragm 31 b shown in FIG. 3B, the light-shieldingplate 37 b serving as the light-shielding member is provided with anopening. In the example of this figure, the light-shielding area alsochanges with a downward movement of the light-shielding plate 37 b as inthe example of FIG. 3A. In other words, an increase in the distancebetween centers of the opening of the light-shielding plate 37 b and theopening of the fixed diaphragm 36 enlarges the light-shielding area. Inthe example shown in this figure, the shielded portion surrounded by theinternal circumference of the opening of the light-shielding plate 37 band that of the opening of the fixed diaphragm 36 has a substantiallycrescent shape.

With regard to the diaphragm 31 c shown in FIG. 3C, the light-shieldingplate 37 c serving as the light-shielding member is provided with anopening. The diameter of the opening of the light-shielding plate 37 ccan be changed so as to change the light-shielding area. In other words,as shown in this figure, a decrease in the opening diameter of thelight-shielding plate 37 c enlarges the light-shielding area. In theexample shown in this figure, the shielded portion surrounded by theinternal circumference of the opening of the light-shielding plate 37 cand that of the opening of the fixed diaphragm 36 also has asubstantially crescent shape as in the example of FIG. 3B.

When the diaphragm 31 a shown in FIG. 3A is taken as an example, in thecase where the side 37 d of the light-shielding plate 37 a is locatedabove the opening of the fixed diaphragm 36, the light-shielding area iszero. In this case, the illuminating light 32 and unwanted reflectionlight 35 generated at an interface of the cover glass of the reflectinglight valve 6 come closest to each other in FIG. 1. In other words, inthis case, the largest amount of unwanted reflection light enters theprojection lens 7.

When shielding light, the light-shielding area changes along themovement of the light-shielding plate 37 a in a direction indicated byan arrow 40. In other words, moving the lower side 37 d from a referenceposition toward the optical axis 12 and keeping it moving in thisdirection enlarges the light-shielding area continuously, so that theopening of the fixed diaphragm 36 is shielded gradually downward, wherethe reference position is a position of the light-shielding member atwhich the periphery of the illuminating light 32 and that of thereflection light 35 come closest to each other. Also, in the state wherethe shielded portion is formed, moving the lower side 37 d in adirection facing opposite to the arrow 40 reduces the light-shieldingarea, so that the opening of the fixed diaphragm 36 is opened in onedirection.

By the movement in the direction indicated by the arrow 40, the unwantedreflection light 35 in FIG. 1 is cut gradually from the side of theoptical axis. In other words, although the movement of the lower side 37d of the light-shielding plate 37 a in the direction indicated by thearrow 40 enlarges the light-shielding area, the shielded portionenlarges gradually from the top of the fixed diaphragm 36 and the lowerportion of the opening of the fixed diaphragm 36 remains open becausethe shape of the shielded portion is rotationally asymmetric to theoptical axis.

Accordingly, shielding of necessary light can be better avoided comparedwith a diaphragm for changing the light-shielding area in a rotationallysymmetric manner, for example, a diaphragm for narrowing the openingconcentrically, making it possible to improve contrast performance whileminimizing brightness reduction.

As the moving system for moving the light-shielding plate, it isappropriate to use a structure in which the light-shielding plate isattached to a rotational shaft of a motor via a gear so that thelight-shielding plate is displaced relative to the rotation of themotor, for example. In this case, the light-shielding area may becontrolled by controlling the rotation of the rotational shaft so as tostop the light-shielding plate at a desired position.

The light-shielding area is enlarged by moving the entirelight-shielding plate in the examples of FIGS. 3A and 3B, whereas thelight-shielding area is enlarged by changing the opening area of thelight-shielding plate 37 c while the light-shielding plate 37 c is beingfixed in the example of FIG. 3C. The mechanisms of the light-shieldingplate 37 c with a changeable opening area and the moving system may bethose similar to an iris diaphragm, for example.

Furthermore, it is desired that the material for the light-shieldingplates 37 a to 37 c shown in FIG. 3 have a surface reflectance of atleast 80%. The reason is that, since light with a high energy enters theshielded portion, as more light is absorbed in the surface of theshielded portion, an increase in the light-shielding area raises thetemperature of the shielded portion, so that radiant heat may damageperipheral optical components.

In the present embodiment, an aluminum plate with a mirror-finishedsurface whose reflectance was about 88% was used. However, there is noparticular limitation to the above, and an article of metal such asstainless steel with a mirror-finished surface or a mirror elementobtained by forming a dielectric multilayer film on the surface of abase also may be used.

FIGS. 4A and 4B are graphs showing the relationship between alight-shielding amount of a diaphragm and a projected image performancein the projection-type display apparatus according to the presentembodiment. FIG. 4A shows the relationship between the light-shieldingamount of the diaphragm (the axis of abscissa S) and a contrast ratio(the axis of ordinate C), while FIG. 4B shows the relationship betweenthe light-shielding amount of the diaphragm (the axis of abscissa S) andan optical output relative value (the axis of ordinate P). As thesegraphs indicate, an increase in the light-shielding amount of thediaphragm S raises the contrast ratio C and lowers the optical output P.In other words, the contrast ratio and the optical output of theprojected image with respect to the light-shielding amount of thediaphragm are in a reciprocal relationship.

Accordingly, it is appropriate to provide an input means outside theapparatus and a control system for controlling the displacement amountby the moving system so that the light-shielding area of the diaphragmcan be controlled from outside of the apparatus by remote control. Withthis configuration, the balance between the contrast and the opticaloutput can be designed suitably as necessary.

For instance, in the example of FIG. 3A, moving the light-shieldingplate 37 a in the direction indicated by the arrow 40 can enlarge thelight-shielding area, which lowers the optical output but improves thecontrast. Conversely, moving the light-shielding plate 37 a in thedirection facing opposite to the arrow 40 can enlarge the opening of thediaphragm, which lowers the contrast but improves the optical output.With this configuration, it is possible to select suitably a projectedimage in which the brightness is important or that in which the contrastis important according to an intended use.

Moreover, using the above-described control system, the light-shieldingarea of the diaphragm may be controlled automatically according to thelevel of the video signal. For example, by giving priority to thecontrast and the higher level of black in darker scenes and givingpriority to the higher level of white in brighter scenes, it is possibleto obtain a display performance with enhanced contrast.

SECOND EMBODIMENT

FIG. 5 shows a schematic configuration of a projection-type displayapparatus according to a second embodiment of the present invention. Inthis figure, the lamp 1 serving as a light source, the reflecting lightvalve 6 and the projection lens 7 are equivalent to those shown inFIG. 1. Also, an optical system constituted by a concave mirror 2, a rodprism 3, a condenser lens 4, a reflecting mirror 42, a field lens 43 anda total reflection prism 44 is collectively called an illuminatingoptical system.

The concave mirror 2, the rod prism 3 and the condenser lens 4 have thesame effects as in the embodiment described referring to FIG. 1, andtherefore, the description thereof will be omitted. In the presentembodiment, light that has left the condenser lens 4 travels via thereflecting mirror 42 and the field lens 43 and reaches the totalreflection prism 44.

Here, the effect of the total reflection prism 44 will be described. Thetotal reflection prism 44 is constituted by two prisms, and a very thinair layer 45 is formed between their adjacent surfaces. The angle of theair layer 45 is designed so that illuminating light 46 entering the airlayer 45 at an angle of at least a critical angle is totally-reflectedand enters the reflecting light valve 6 obliquely, and ON light 47 as aprojected image enters the air layer 45 at an angle of not greater thanthe critical angle, passes therethrough and reaches the projection lens7. By designing the total reflection prism 44 in an optical path of theilluminating optical system as described above, a compact illuminatingoptical system can be constructed.

The ON light 47 corresponding to a white display in the illuminatinglight 46 that has entered the reflecting light valve 6 passes throughthe total reflection prism 44 and the projection lens 7 and then ismagnified and projected onto a screen (not shown). On the other hand,OFF light 48 corresponding to a black display travels outside aneffective diameter of the projection lens 7 and does not reach thescreen.

In the present embodiment, not only first unwanted reflection light 49generated at an interface of a cover glass of the reflecting light valve6, but also second unwanted reflection light 50 generated at aninterface on the reflecting light valve 6 side of the total reflectionprism 44 affects the contrast performance of the projected image. Inthis case, the degree of influence of the first unwanted reflectionlight 49 and the second unwanted reflection light 50 that enter theprojection lens 7 also can be changed suitably by a diaphragm 41 whoselight-shielding area can be changed.

The shape of the opening of the diaphragm 41 also can be changed byusing the mechanism illustrated in FIG. 3 as in the first embodiment.Stopping down and opening by the change in the shielded portion aresimilar to those in the first embodiment, that is, moving thelight-shielding member from the reference position toward the opticalaxis 12 and keeping it moving in this direction enlarges thelight-shielding area continuously, so that the opening of the diaphragm41 is shielded gradually from one side. Also, in the state where theshielded portion is formed, moving the light-shielding member in theopposite direction reduces the light-shielding area, so that the openingof the diaphragm 41 is opened in one direction.

FIG. 6 shows a schematic configuration of a projection-type displayapparatus according to a comparative example of the embodiment shown inFIG. 5. In the comparative example shown in FIG. 6, the diaphragm 41 isnot provided, or the opening of the diaphragm 41 is open. In this case,after illuminating light 51 enters the reflecting light valve 6, ONlight 52 corresponding to the white display passes through the totalreflection prism 44 and the projection lens 7 and then is magnified andprojected onto the screen (not shown). On the other hand, OFF light 53corresponding to the black display travels outside the effectivediameter of the projection lens 7 and does not reach the screen.

Further, first unwanted reflection light 54 and second unwantedreflection light 55 both cause the deterioration of the contrastperformance of the projected image. When the embodiment of FIG. 5 andthe comparative example of FIG. 6 are compared, it can be seen that rayfluxes of the first unwanted reflection light 49 and the second unwantedreflection light 50 shown in FIG. 5 are thinner than those of the firstunwanted reflection light 54 and the second unwanted reflection light 55shown in FIG. 6 because a part of the opening of the fixed diaphragm isshielded using the diaphragm 41 in FIG. 5.

As described above, in the embodiment of FIG. 5, both of the firstunwanted reflection light 49 and the second unwanted reflection light 50can be cut by the diaphragm 41 more effectively than in the comparativeexample shown in FIG. 6. In other words, shielding of necessary lightcan be better avoided compared with a diaphragm for changing theshielded area in a rotationally symmetric manner, for example, adiaphragm for narrowing the opening concentrically, making it possibleto improve contrast performance while minimizing brightness reduction.

In addition, the arrangement of the diaphragm 41 and the material forthe light-shielding plate are similar to those in the first embodiment.Furthermore, similarly to the first embodiment, it is preferable thatthe light-shielding area of the diaphragm can be controlled from anoutside of the set by remote control and that the light-shielding areacan be controlled according to a video signal. Additionally, althoughthe change in the light-shielding area of the diaphragm 41 has beendescribed by the example of moving the light-shielding member, theopening of the light-shielding member may be changed as in the structureof FIG. 3C.

THIRD EMBODIMENT

FIG. 7 shows a schematic configuration of a projection-type displayapparatus according to a third embodiment of the present invention. Inthis figure, the lamp 1 serving as a light source, the reflecting lightvalve 6 and the projection lens 7 are equivalent to those shown inFIG. 1. Also, as in FIG. 5, a system constituted by a concave mirror 2,a rod prism 3, a condenser lens 4, a reflecting mirror 42, a field lens43 and a total reflection prism 44 is collectively called anilluminating optical system.

The concave mirror 2, the rod prism 3 and the condenser lens 4 have thesame effects as in the embodiment described referring to FIG. 1, andtherefore, the description thereof will be omitted. In the presentembodiment, a color separation/combination prism 62 is disposed betweenthe total reflection prism 44 and the reflecting light valve 6, andthree reflecting light valves 6 are used.

In the following, the structure and effect of the colorseparation/combination prism 62 will be described referring to FIG. 8.FIG. 8 is a horizontal sectional view showing the colorseparation/combination prism 62 shown in FIG. 7. The colorseparation/combination prism 62 is constituted by three prisms, and thecontact surfaces thereof are provided with a first dichroic mirror 71and a second dichroic mirror 72. In the case of the colorseparation/combination prism 62 used in the present embodiment, out oflight 73 that has entered from the total reflection prism 44, only bluelight is reflected first by the first dichroic mirror 71 so that bluelight 74 is generated and enters a blue-reflecting light valve 6B.

Next, only red light is reflected by the second dichroic mirror 72 sothat red light 75 is generated and enters a red-reflecting light valve6R. Then, green light 76 that has passed through both the first dichroicmirror 71 and the second dichroic mirror 72 enters a green-reflectinglight valve 6G. These three colors of light are reflected by theircorresponding reflecting light valves 6B, 6R and 6G and then combinedinto one again by the first dichroic mirror 71 and the second dichroicmirror 72, so as to enter the total reflection prism 44.

As described above, white light is separated into three primary colorsof red, blue and green and then combined, and three reflecting lightvalves 6B, 6R and 6G corresponding to respective video signals are used,thereby displaying a high-resolution full-color projected image. ONlight 64 corresponding to the white display in illuminating light 63that has entered the reflecting light valve 6 shown in FIG. 7 passesthrough the color separation/combination prism 62, the total reflectionprism 44 and the projection lens 7 and then is magnified and projectedonto a screen (not shown). On the other hand, OFF light 65 correspondingto the black display travels outside an effective diameter of theprojection lens 7 and does not reach the screen.

In the present embodiment, not only the unwanted reflection lightgenerated at the interface of the cover glass of the reflecting lightvalve 6 as shown in FIGS. 1 and 5 and the unwanted reflection lightgenerated at the interface on the reflecting light valve 6 side of thetotal reflection prism 44 as shown in FIG. 5 (both are not shown in FIG.7), but also unwanted reflection light 66 generated at an interface ofthe color separation/combination prism affects the contrast performanceof the projected image.

In this case, the degree of influence of the unwanted reflection light66 that enters the projection lens 7 also can be changed suitably by adiaphragm 61 whose light-shielding area can be changed. The shape of theopening of the diaphragm 61 can be changed by using the mechanismillustrated in FIG. 2 as in the first embodiment. Stopping down andopening by the change in the shielded portion are similar to those inthe first embodiment, that is, moving the light-shielding member fromthe reference position toward the optical axis 12 and keeping it movingin this direction enlarges the light-shielding area continuously, sothat the opening of the diaphragm 61 is shielded gradually from oneside. Also, in the state where the shielded portion is formed, movingthe light-shielding member in the opposite direction reduces thelight-shielding area, so that the opening of the diaphragm 61 is openedin one direction.

FIG. 9 shows a schematic configuration of a projection-type displayapparatus according to a comparative example of the embodiment shown inFIG. 7. In the comparative example shown in FIG. 9, the diaphragm 61 isnot provided, or the opening of the diaphragm is open. In this case,after illuminating light 81 enters the reflecting light valve 6, ONlight 82 corresponding to the white display passes through the colorseparation/combination prism 62, the total reflection prism 44 and theprojection lens 7 and then is magnified and projected onto a screen (notshown).

On the other hand, OFF light 83 corresponding to the black displaytravels outside an effective diameter of the projection lens 7 and doesnot reach the screen. Further, unwanted reflection light 84 causes thedeterioration of the contrast performance of the projected image.

Incidentally, although not shown in the figure, the unwanted reflectionlight generated at the interface of the cover glass of the reflectinglight valve 6 and that generated at the interface of the totalreflection prism 44 also have an influence similar to those in the casesshown in FIGS. 1 and 5.

When the embodiment of FIG. 7 and the comparative example of FIG. 9 arecompared, it can be seen that a ray flux of the unwanted reflectionlight 66 shown in FIG. 5 is thinner than that of the unwanted reflectionlight 84 shown in FIG. 9 because a part of the opening of the fixeddiaphragm is shielded using the diaphragm 61 in FIG. 7.

As described above, in the embodiment of FIG. 7, the unwanted reflectionlight 66 can be cut by the diaphragm 61 more effectively than in thecomparative example shown in FIG. 9. In other words, shielding ofnecessary light can be better avoided compared with a diaphragm forchanging the shielded area in a rotationally symmetric manner, forexample, a diaphragm for narrowing the opening concentrically, making itpossible to improve contrast performance while minimizing brightnessreduction.

In addition, the arrangement of the diaphragm 61 and the material forthe light-shielding plate are similar to those in the first embodiment.Furthermore, similarly to the first embodiment, it is preferable thatthe light-shielding area of the diaphragm can be controlled from anoutside of the set by remote control and that the light-shielding areacan be controlled according to a video signal. Additionally, althoughthe change in the light-shielding area of the diaphragm 61 has beendescribed by the example of moving the light-shielding member, theopening of the light-shielding member may be changed as in the structureof FIG. 3C.

Although the above-described embodiments have been directed to theconfiguration in which the light-shielding area of the diaphragm can bechanged in order to adjust the contrast performance and the opticaloutput suitably, it also may be possible to adopt the configuration inwhich the opening of the diaphragm is fixed to achieve a certain desiredcontrast performance. In such a configuration, the moving system is notneeded, and the shape of the opening is equivalent to a remaining shapeafter removing the shielded portion (hatched portion) from the openingin the fully opened state in the examples of FIGS. 3A to 3C.

In other words, the shape of the fixed opening is equivalent to a shapeobtained by shielding a portion that is rotationally asymmetric to theoptical axis such as a substantially part-circular shape or asubstantially crescent shape over the opening in the fully opened state.In this case, since the portion corresponding to the shielded portionhas a shape that is rotationally asymmetric to the optical axis, theshape of the fixed opening also is rotationally asymmetric to theoptical axis.

Although the diaphragms are provided at a substantially conjugateposition of the entrance pupil of the projection lens in the opticalpath of the illuminating optical system in the above-describedembodiments, they also may be disposed directly at the entrance pupil ofthe projection lens to obtain a similar effect.

Furthermore, the diaphragms used in the above-described embodiments aremost effective for light valves on which an optical image is formed bycontrolling the traveling direction of light according to a video signalsuch as the reflecting light valve shown in FIG. 11. However, there isno particular limitation to such reflecting light valves, and the effectof reducing the unwanted reflection light can be obtained as long as itis a reflecting light valve having a transparent glass or plastic sheeton an exit side of its image formation surface. For example, a lightvalve of a type in which a liquid crystal or the like is used as amodulating material and an optical image is formed based on changes in apolarization state, a diffraction state or a scattering state of light.

Industrial Applicability

As described above, according to the present invention, the shape of theportion shielded by the light-shielding member is made rotationallyasymmetric to the optical axis of the illuminating optical system,making it possible to improve contrast performance while suppressingshielding of necessary light so as to minimize brightness reduction,which can be applied to a projection-type display apparatus thatmagnifies an optical image formed on a light valve and projects it ontoa screen.

1. A projection-type display apparatus comprising: a light source; areflecting light valve for controlling a traveling direction of areflected light with respect to an incident illuminating light accordingto a signal; an illuminating optical system for focusing a light fromthe light source onto the reflective light valve; a projection lens formagnifying and projecting the light from the reflecting light valve ontoa screen; and a diaphragm disposed at a position relative to an entrancepupil of the projection lens or a substantially conjugate position ofthe entrance pupil and provided with an opening for shielding a part ofthe radiant light from the light source, the diaphragm including a fixeddiaphragm having an opening and a movable light-shielding plate forshielding at least a part of the opening of the fixed diaphragm; whereinthe movable light-shielding plate is operable to shift a centroid of theopening of the diaphragm away from an optical axis of the projectionlens or the illuminating optical system so as to suppress a projectionof a reflection light reflected by a front surface of the reflectinglight valve onto a screen.
 2. The projection-type display apparatusaccording to claim 1, comprising a prism for both reflecting anilluminating light from the illuminating optical system toward thereflecting light valve and transmitting the reflected light from thereflecting light valve.
 3. The projection-type display apparatusaccording to claim 1, wherein the number of the reflecting light valvesis three, and the projection type display apparatus further comprises afirst prism for reflecting an illuminating light from the illuminatingoptical system toward the reflecting light valves and transmitting thelight from the reflecting light valves, and a second prism forseparating the illuminating light into three components of primarycolors of red, blue and green and combining into one the threecomponents that are reflected by the corresponding reflecting lightvalves.
 4. The projection-type display apparatus according to claim 1,wherein the reflecting light valve has an image formation surface and atransparent plate that is disposed on an exit side of the imageformation surface and in parallel with the image formation surface. 5.The projection-type display apparatus according to claim 1, wherein thereflecting light valve is formed of a plurality of mirror elements thatare arranged in a matrix pattern and control a reflecting direction oflight according to a video signal.
 6. The projection-type displayapparatus according to claim 1, wherein the diaphragm is constituted bythe movable light-shielding plate having at least one straight side andthe fixed diaphragm having a circular opening.
 7. The projection-typedisplay apparatus according to claim 1, wherein the diaphragm isconstituted by the movable light-shielding plate having a circularopening and the fixed diaphragm having a circular opening.
 8. Theprojection-type display apparatus according to claim 1, wherein thediaphragm is constituted by the movable light-shielding plate having acircular opening whose diameter is changeable and the fixed diaphragmhaving a circular opening, and a centroid of the opening of the movablelight-shielding plate is shifted from the opening of the fixeddiaphragm.
 9. The projection-type display apparatus according to claim1, further comprising a moving system for moving the movablelight-shielding plate, a control system for controlling how much themovable light-shielding plate is displaced by the moving system, whereinan opening area of the diaphragm is controlled automatically accordingto a level of an input video signal.
 10. A projection-type displayapparatus comprising: a light source; a diaphragm having an opening andshielding a part of a light; a reflecting light valve having a mirrorelement for reflecting a light from the light source; and a projectionlens; wherein the mirror element has an inclination angle that ischangeable so as to reflect an incident light in a first direction forallowing the incident light to enter the projection lens or a seconddirection for not allowing the incident light to enter the projectionlens, and a centroid of the opening is shifted from an optical axis ofthe light from the light source so that a part of a flux of rays of thelight reflected in the second direction at a position close to theprojection lens is cut off.
 11. The projection-type display apparatusaccording to claim 10, wherein the opening of the diaphragm has a shapesurrounded by a circular arc and a straight line.
 12. Theprojection-type display apparatus according to claim 10, wherein theopening of the diaphragm has a shape of an overlapping portion of twocircles.
 13. A projection-type display apparatus comprising: a lightsource; a reflecting light valve having a mirror element for reflectinga light from the light source; a diaphragm having an opening andshielding a part of a light; and a projection lens; wherein the mirrorclement has an inclination angle that is changeable so as to reflect anincident light in a first direction for allowing the incident light toenter the projection lens or a second direction for not allowing theincident light to enter the projection lens, and a centroid of theopening is shifted from an optical axis of the light reflected in thefirst direction towards a position further away from the light reflectedin the second direction.
 14. The projection-type display apparatusaccording to claim 13, wherein the opening of the diaphragm has a shapesurrounded by a circular arc and a straight line.
 15. Theprojection-type display apparatus according to claim 13, wherein theopening of the diaphragm has a shape of an overlapping portion of twocircles.
 16. A projection-type display apparatus comprising: a lightsource; a diaphragm having an opening and shielding a part of a light; areflecting light valve having a mirror element for reflecting a lightfrom the light source; and a projection lens; wherein the mirror elementhas an inclination angle that is changeable so as to reflect an incidentlight in a first direction for allowing the incident light to enter theprojection lens or a second direction for not allowing the incidentlight to enter the projection lens, the opening has a first edge portionand a second edge portion that face each other with an optical axis ofthe light from the light source located therebetween, and a distancebetween the first edge portion and the optical axis is smaller than thatbetween the second edge portion and the optical axis, and the light thatpasses near the first edge portion and is reflected in the seconddirection at the reflecting light valve constitutes a part closer to theprojection lens than the light that passes near the second edge portionand is reflected in the second direction at the reflecting light valve.17. The projection-type display apparatus according to claim 16, whereinthe opening of the diaphragm has a shape surrounded by a circular arcand a straight line.
 18. The projection-type display apparatus accordingto claim 16, wherein the opening of the diaphragm has a shape of anoverlapping portion of two circles.
 19. A projection-type displayapparatus comprising: a light source; a reflecting light valve having amirror element for reflecting a light from the light source; a diaphragmhaving an opening and shielding a part of a light; and a projectionlens; wherein the mirror element has an inclination angle that ischangeable so as to reflect an incident light in a first direction forallowing the incident light to enter the projection lens or a seconddirection for not allowing the incident light to enter the projectionlens, and the opening has a first edge portion and a second edge portionthat face each other with an optical axis of the projection lens locatedtherebetween, a distance between the first edge portion and the opticalaxis is smaller than that between the second edge portion and theoptical axis, and the first edge portion is closer than the second edgeportion to the light reflected in the second direction.
 20. Theprojection-type display apparatus according to claim 19, wherein theopening of the diaphragm has a shape surrounded by a circular arc and astraight line.
 21. The projection-type display apparatus according toclaim 19, wherein the opening of the diaphragm has a shape of anoverlapping portion of two circles.